is email server software
responsible for message delivery. Messages from firstname.lastname@example.org usually indicate a problem with the recipient's mail server or address. For example, a common problem that causes a mailer Daemon message is sending a message to an incorrect e-mail address. You may receive email bounce-back messages from mailer-daemon that were not yours to begin with, but unsolicited commercial email
bounce-backs. If you send legitimate email to a valid account and still get responses back from mailer-daemon, your domain
may be on a blacklist.
Daemon (computer software)